The present invention is related to an improved screw which can be more quickly screwed into a work piece and can more smoothly exhaust the chips of the work piece. The screw has a rod body and higher thread and lower thread formed on the rod body. Alternatively, the screw can have single thread or double threads with equal height. On a predetermined section of the rod body of the screw, a cutting thread with changed guide angle is directly formed as a part of the thread to achieve better cutting, drilling and chip-exhausting function.
Different types of screws have different structures according to the qualities of the work pieces in which the screws are screwed. However, with respect to all types of screws, it is required that the screws can be quickly firmly screwed into the work pieces with less strength. The screwing speed and the torque necessary for screwing the screw into the work piece are directly affected by whether the drilling chips of the work piece can be smoothly exhausted. In the case that the thread of the screw is designed with such a chip-exhausting structure as to smoothly exhaust the chips, the screw can be quickly screwed into the work piece with less torque. Reversely, the screw will encounter a greater resistance. As a result, the screw can be hardly quickly screwed into the work piece and the necessary torque is greater.